"HTML5 defines a standard way to embed video in a web page, using a video element. Support for the video element is still evolving, which is a polite way of saying it doesn't work yet. At least, it doesn't work everywhere. But don't despair! There are alternatives and fallbacks and options galore."

What is the problem is that you need to pay license fees to actually use it. If you provide it in source-only form then the consensus is that you don't need to pay any fees but if you provide binaries, you need to pay fees. To address this, Google pays the license for Chrome even though they don't charge their users whereas Chromium, the open source project, doesn't pay any fees and isn't allowed to distribute the AVC codec in binary form and apparently doesn't provide it in source form either.